The present invention is in the field of air control valves; more particularly, the invention relates to an air control valve for use in a tractor-trailer air brake system.
Tractor-trailer rigs are equipped with air activated brake systems which incorporate structural features enabling them to meet requirements of the government and the trade. Federal Motor Vehicle Safety Standard (FMVSS) No. 121 makes two broad requirements affecting the use of valves to control tractor-trailer air brake systems. The first requirement, Section 5.1.3-Towing Vehicle Protection System, states: "If the vehicle is intended to tow another vehicle equipped with air brakes, a system to protect the air pressure in the towing vehicle from the effects of a loss of air pressure in the towed vehicle." The second requirement, Section 5.6.4-Parking Brake Control--Trucks and Buses, states, "The parking brake control shall be separate from the service brake control. It shall be operable by a person seated in the normal driving position. The control shall be identified in a manner that specifies the method of control operation. The parking brake control shall control the parking brakes of the vehicle and of any air braked vehicle that it is designed to tow." FMVSS-121 also requires that the tractor and trailer parking brakes must apply when the tractor-trailer park control valve (hereinafter PV) is set when parking the rig.
In summary, when an air parking brake control system is used, the parking brake control must be separate from the service brake control. The parking brake control must control the parking brakes of the towing vehicle and any vehicle which is being towed. The air pressure in the towing vehicle must be protected from a loss of air pressure in the towed vehicle.
Prior art systems have been developed and are in use which comply with these federal requirements. Generally, the systems use three control valves which are interconnected in the air system. Pressure in the system releases the braking actuators, releasing the brakes. Example systems are described in U.S. Pat. Nos. 4,088,374 and 3,929,381. As stated above, there must be a PV to apply the tractor and trailer brakes.
A second valve used to meet the above requirements is a tractor protection control valve (hereinafter known as TPCV) which plugs the tractor system from leakage through the trailer connections during bobtail tractor operation, or when the tractor to trailer air line ruptures.
Initially, only the PV and TPCV were used to conform to the regulations. A rig having only a TPCV and PV would roll freely if parked on an incline when an attempt was made to pressurize the trailer system. It was found during pressurizing that all the brakes of the rig were released at an intermediate pressure and, unless the operator was in the seat ready to use pedal control, the rig was free to roll. At this stage of development, a tractor only park valve (hereinafter a TOPV) was designed and incorporated into the system so that the trailer air system could be filled while the tractor brakes were securely set during the pressurizing operation. A truck operator now has mounted within easy reach, three valves consisting of a TPCV, a PV and a TOPV.
The three valves presently used to accomplish the federally required air parking braking operation result in a complicated system. Because of this complicated parking brake operation, drivers ignore it or operate it incorrectly. It is desirable to provide an air brake operating system meeting all of the federal requirements which is simpler to operate. Further, it is desirable to develop a valve which can accomplish simple operation of the air braking system which itself is simpler to operate and easier to construct.